(1) Field of the Invention
The present invention relates to a method for detecting a position of a defect such as chipping or cracking that occurs at an outer periphery of a semiconductor wafer.
(2) Description of the Related Art
In order to detect a center position of a semiconductor wafer, conventionally, there has been utilized a detecting device of a light transmission type. The detecting device includes a light projector and a light receiver disposed so as to be opposed to each other with a peripheral edge of the semiconductor wafer being placed therebetween. Specifically, the detecting device detects an alignment part such as a notch or an orientation flat formed at the peripheral edge of the semiconductor wafer. As a method for obtaining the center position of the semiconductor wafer on the basis of the detected position, there has been known a detecting method of a light transmission type (refer to, for example, JP-A 08-279547).
There has been also known a detecting method of a light reflection type. This method involves: receiving, at an image capturing camera, a light beam which is emitted to a surface of a semiconductor wafer and, then, is reflected from the surface of the semiconductor wafer; and determining a position of a notch on the basis of data of images captured by the image capturing camera (refer to, for example, JP-A 2003-258062).
However, the detecting method of the light transmission type has the following problems. In a case where a protective tape is joined to a pattern formation side of a semiconductor wafer, a metal film is deposited on or dust is attached to the protective tape at a portion corresponding to the notch in a previous process. Consequently, a light transmittance is lowered at the notch, so that the notch cannot be detected with accuracy.
On the other hand, the detecting method of the light reflection type has the following problems. A light beam emitted to a surface of a semiconductor wafer is reflected irregularly in some cases depending on a state of the surface of the semiconductor wafer. An image of a notch becomes blurred due to an influence of the irregular reflection, so that the notch cannot be detected with accuracy. According to the conventional method, particularly, a portion corresponding to a semiconductor wafer is represented in black and a remaining portion is represented in white in data of a captured image.
Accordingly, there is a problem that a defect such as minute chipping smaller than a notch or cracking on a surface of a semiconductor wafer cannot be detected.